160 Mr. C. C. Dobell. Observations on the [Nov. 19, 



Since then, many other " chromidial " nuclear phenomena have been 

 described. Indeed, it is now a matter of some difficulty to give a definition 

 of chromidia which will embrace all conditions so described. In its widest 

 sense, the term is applied to all chromatin substance (i.e., all matter which 

 takes up nuclear stains) which lies within the cell and which is not gathered 

 together in the form of a definite nucleus. Chromatin granules of diverse 

 shapes and sizes, strands, networks — all these come in this category ; and, 

 moreover, the physiology of these structures seems to be no less heterogeneous 

 than their morphology. For chromidia seem to be formed sometimes as the 

 result of degeneration, sometimes as a form of nuclear division, sometimes as 

 katabolic products of nuclear activity — sometimes (as in bacteria), being the 

 normal vegetative stage of the neucleus — and so on. 



Many new terms have been introduced for these various forms of 

 chromidia. Since many of these have not received general acceptance, and 

 since many are, I think, quite unjustifiable, owing to our present ignorance 

 of the causes underlying the different phenomena, I have used but two terms 

 in my description of the nuclear changes in A. ovata, — " chromidia " for 

 separate chromatin granules lying in the cytoplasm, and " chromidial net " for 

 a collection of chromatin granules united by a reticulum. Amongst the 

 terms which are more frequently met with in papers on this subject the 

 following may be mentioned : — The name " Sporetium " (Goldschmidt) has 

 been given to chromidial structures formed previous to gamete formation. 

 " Protogonoplasm " (Calkins) and " Idiochromidium " (Goldschmidt) are other 

 terms applied to the same structures. Then, again, we have such terms as 

 " Trophochromidium " and " Ghromidium " (sensu stricto) applied by Gold- 

 schmidt to chromidial structures of a vegetative (as opposed to reproductive) 

 nature. Other terms, such as " distributed nucleus " (Calkins), etc., require 

 no special explanation. 



A chromidial condition of the nucleus may occur, apparently, not only in 

 all the chief subdivisions of the Protozoa, but also in some Metazoa and in 

 Bacteria. 



The great interest which attaches to chromidia arises from the fact that 

 investigation of these structures has revealed a " Doppelkernigkeit," or 

 nuclear dimorphism, in many Protozoa. That is to say, two distinct elements 

 can be recognised in many protozoan nuclei — one, a " propagative" element, 

 the other, a " somatic" The propagative seems specially liable to separate 

 from the somatic as chromidia (cf. Schaudinn, Neresheimer, etc.). The 

 heterokaryote condition of the Ciliata thus finds a parallel in many other 

 Protozoa. To the single nucleus, combining the chromatic elements proper 

 both to the soma and reproduction, is given the name " amphinucleus." 



